Phosphatidylcholine and phosphatidylinositol exchange proteins in pig liver

The pH 5.1 supernatant fraction of pig liver homogenate stimulated the transfer of [32P]phosphatidylcholine and [32P]phosphatidylinositol from donor liposomes to acceptor liposomes. Purification of the proteins which catalyzed the exchanges yielded five partially purified preparations. A phospholipid exchange protein was purified 63-fold in one of the preparations and the protein was found to be specific for phosphatidylcholine exchange. The molecular weight and isoelectric point of the protein was estimated to be 19,000 and 5.6, respectively. The other four preparations contained partially purified phospholipid exchange proteins which catalyzed the exchanges of phosphatidylinositol as well as phosphatidylcholine. The molecular weights and the isoelectric points of the phosphatidylcholine-phosphatidylinositol exchange proteins were estimated to be 19,000 and 4.7, and 19,000 and 4.8 for the proteins in the second preparation, and 21,000 and 4.5 for the protein in the third preparation. These parameters in the other two preparations were tentatively estimated to be 24,000 and 5.6, and 18,000 and 4.6. Neither sulfhydryl-binding reagents nor trypsin digestion inactivated the activity of the phosphatidylcholine specific exchange protein. Sulfhydryl-binding reagents and trypsin digestion inactivated all the phosphatidylinositol exchange activities of the partially purified exchange proteins and the phosphatidylcholine exchange activities which were presumably associated with the phosphatidylinositol exchange proteins.

Measurement of isoelectric points of phospholipid exchange proteins by gel isoelectric focusing

A method of the estimation of isoelectric points of phospholipid exchange proteins is described. The phospholipid presumably bound to a phospholipid exchange protein was replaced with [3H]phosphatidylcholine of a high specific radioactivity by an incubation of the protein with liposomes containing the labeled lipid and dimannosyl diglyceride. After the incubation, a major portion of the liposomes was separated from the protein by an affinity of the liposomes to concanavalin A-Sepharose 2B. The isoelectric point of the protein was measured by gel isoelectric focusing of the protein, which was located by tritium radioactivity of the bound [3H]phosphatidylcholine. The method was used to measure isoelectric points of partially purified phospholipid exchange proteins in pig liver.

A simple and effective method for hemolysis with a hypoxanthine-xanthine oxidase system and alteration of erythrocyte phospholipid composition during the hemolysis

A very rapid hemolysis was found to be caused by active oxygen species produced by a hypoxanthine-xanthine oxidase system with very low concentrations of hypoxanthine. The addition of superoxide dismutase or catalase inhibited the hemolysis, indicating that O2- and H2O2 participate in this system. The extent of erythrocyte hemolysis was found to depend on the sex of the human donor. The change in phospholipid composition before and after hemolysis in human erythrocytes from donors of each sex was compared by thin layer chromatography. A significant decrease in phosphatidylethanolamine content and a concomitant increase in altered phospholipid fraction were observed in erythrocytes from male donors, suggesting that these erythrocytes were easily attacked by active oxygen species to produce modified phosphatidylethanolamine.

Phosphatidylcholine and phosphatidylinositol exchange proteins in rat liver

The phospholipid exchange proteins in rat liver that stimulate the transfer of phosphatidylcholine and phosphatidylinositol between membranes were separated into three fractions and partially purified by acid pH precipitation, gel filtration on Sephadex G-75, and ionexchange chromatography on DEAE-cellulose and CM-cellulose. Throughout the steps of the purification, both the phosphatidylcholine exchange activity and the phosphatidylinositol exchange activity were measured by a liposome-liposome assay system, which used concanavalin A in the separation of donor and acceptor liposomes. One of the fractions was purified 172-fold and stimulated the phosphatidylcholine exchange but not the phosphatidylinositol exchange. The other two fractions were active in the stimulation of the phosphatidylinositol exchange as well as the phosphatidylcholine exchange and were purified 62-fold and 58-fold over the cell supernatant fraction with respect to the phosphatiylinsitol exchange activity. These two fractions stimulated the transfer of phosphatidylinositol from donor liposomes to acceptor liposomes initially deficient in this phospholipid.

A new assay system of phospholipid exchange activities using concanavalin A in the separation of donor and acceptor liposomes

A new assay system of phospholipid exchange activities is described. The exchange activities were quantitated by measuring the stimulation of phospholipid transfer between two separate populations of liposomes, which contained, as the major constituents, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, sphingomyelin, and cholesterol in molar ratios of 6 :2 : 1: 1: 5. One population of the liposomes was made reactive to concanavalin A by the incorporation of 1.8 mol% alpha-D-mannosyl-(1 leads to 3)-alpha-D-mannosyl-sn-1, 2-diglyceride from Micrococcus lysodeikticus. The concanavalin A-reactive liposomes, a phospholipid donor, were doubly labelled with [6-3H] galactosylglucosyl ceramide and that class of 32P-labelled phospholipids whose exchange was being measured. The 3H-labelled glycolipid served as a non-exchangeable reference marker. The other population of the liposomes, a phospholipid acceptor, was concanavalin A nonreactive. These two populations of liposomes were incubated with the cytosol protein of rat liver in a total volume of 0.2 ml. After the incubation, two different procedures were used to separate the two liposomal populations. In one procedure concanavalin A was added to agglutinate the reactive liposomes; the flocculated lectin . liposome complex was separated from the non-reactive liposomes by brief centrifugation. In the other procedure the reactive liposomes were trapped by binding to concanavalin A covalently coupled to Sepharose 2B; the complex was separated from the non-reactive liposomes by filtration through a filter paper under suction. In both assay procedures the amount of phospholipid transferred from the donor to the acceptor liposomes was calculated from the decrease of 32P/3H ratio of the concanavalin A-reactive liposomes during the incubation. By the assasy system it is possible to determine phosphatidylcholine and phosphatidylinositol exchange activities in 100 micrograms of rat liver cytosol protein.

Separation and purification of phospholipid exchange proteins in rat small intestinal mucosa

The cytosol fraction of rat small intestinal mucosa stimulated the transfer of [32P]phosphatidylcholine and [32P]phosphatidylinositol from donor liposomes to acceptor liposomes. The proteins which catalyzed the exchanges were separated into three fractions by gel filtration on a Sephadex G-75 column and chromatography on DEAE-cellulose and CM-cellulose. One of the fractions was purified 340-fold and stimulated phosphatidylcholine exchange but not phosphatidylinositol exchange. The other two fractions were active in the stimulation of phosphatidylcholine exchange as well as phosphatidylinositol exchange. These two fractions were purified 35-fold and 44-fold over the cytosol fraction with respect to the phosphatidylinositol exchange activity.

Three cases of GM1-gangliosidosis

A biochemical analysis was carried out on three cases of GM1-gangliosidosis which showed different clinical manifestations. These cases were classified in a previous study as Type 1, Type 2 (2B) and Type 2 (2A), an intermediate type between classical Type 1 and Type 2 (2B), by the determination of the chromatographic profile of the liver beta-galactosidase activities. Gangliosides, neutral glycolipids; phospholipids and glycopeptides were analyzed in the brain and the liver of these cases. The concentration of total ganglioside was increased in the brain in all cases. The elevation was due to an increase of GM1-ganglioside, which accounted for 63% or more of the total ganglioside, while in the control brain about 20% of the total ganglioside was GM1-ganglioside. In type 2A, increases of GM1-ganglioside and and asialo-GM1 in the liver were more prominent than those in the liver of Type 2B. The non-dialyzable glycopeptides were analyzed only in Type 2A. In the liver of Type 2A, the hexosamine and hexose contents of the non-dialyzable glycopeptides were about 10 times and 5 times higher than those of the control. These biochemical analyses revealed that Type 2A had intermediate characteristics between two Types. In this classification of the three Types, biochemical data were well correlated with clinical features.

Studies on the composition of phospholipids in rat small intestinal smooth muscle

The phospholipid composition of rat small intestinal smooth muscle was investigated in comparison with those of the mucosa and liver. Phospholipid content per g of the wet smooth muscle was almost identical with that of the mucosa and was about 1/4 of that in the liver. The phospholipid/protein ratio of the smooth muscle was about 1/2 of the value in the liver. Sphingomyelin content was significantly high and amounted to 18% of total phospholipids. This value was about twice that in the mucosa and 4 times higher than that in the liver. On the other hand, the percent distribution of phosphatidylcholine was lowest in the smooth muscle. Distribution patterns of phosphatidylserine and phosphatidylinositol in the smooth muscle as well as in the mucosa were different from those in the liver. The occurrence of vinyl-ether and ether phospholipids was clearly demonstrated in the smooth muscle as well as in the mucosa. A major part of the ether lipids was detected in the phosphatidylethanolamine fraction, in which they amounted to about 50%; 40% as alkenyl-acyl type and 12% as alkyl-acyl type. A high content of ether lipids was also observed in the phosphatidylethanolamine fraction from mucosa, but the distribution was reversed, that is, 14% alkenyl-acyl type and 28% alkyl-acyl type. Fatty aldehydes, fatty alcohols, and fatty acids were also determined by gas-liquid chromatography. The compositions of fatty aldehydes in the phosphatidylethanolamine fraction from smooth muscle and from mucosa were similar, whereas the compositions of long chain fatty alcohol and fatty acids were clearly different. The compositions of fatty alcohols and fatty acids of the phosphatidylcholine fraction from smooth muscle showed significantly different patterns from those of the phosphatidylethanolamine fraction and from those of the same phospholipid fraction in the mucosa.

Exchange of phospholipids between mitochondria and rough or smooth microsomes in vitro

Phospholipids in mitochondria can be exchanged with those in two microsomal fractions from rough endoplasmic reticulum (rough microsomes) and smooth endoplasmic reticulum (smooth microsomes) in vitro in the presence of cell supernatant. The amounts of phospholipids transferred from each submicrosomal fraction to nitochondria were slightly different. The compositions of the phospholipids transferred to mitochondria from both microsomal fractions were the same, though these two fractions actually had different phospholipid compositions.